Bell and spigot ends are commonly provided for pipes or conduit that are adapted to be buried underground. The bell and spigot joining possesses flexibility and provides for expansion and contraction. It is largely used for water and sewer pipe. More recently, it has been used to seal the conduits or ducts used to route telephone and electrical cable underground. Traditionally, bell and spigot end joints are prepared by tightly tamping or inserting a hemp or jute sealant at the bottom of the recess formed between the bell and spigot ends and then pouring in molten lead; after cooling, the lead is calked in tightly to form a gas-tight joint.
While poured joints require no special end preparation of the pipe or close diametrical control during manufacture, they cannot absorb axial movement without leaking. In addition, disassembly must be accomplished by cutting the pipe.
U.S. Pat. No. 3,792,878 by Freeman describes a plastic conduit system wherein adjacent conduit sections are held together by spring clips. Such clips are made of metal. Since they are buried with the conduit underground, these clips can undergo corrosion and deterioration. Eventually they may disintegrate and lose their holding power. Consequently, water and silt can gradually flow into the conduit. In addition, since mechanical and watertight integrity will deteriorate, subsequent settling of the surrounding soil may break the two sections apart resulting in accelerated seepage of water and mud into the entire conduit system. Long-term water-tight integrity is important for conduit systems used to carry telephone and communication cable underground. The invention described herein offers an improved coupling system for such conduit networks, features all plastic construction, increased reliability, and low cost.